Why does RTC 3.0.1.1 sometimes fill in attribute values for no reason?

I have an RTC 3.0.1.1 installation with a custom work item.  This custom work item has a number of custom attributes and there are some calculated values that fill some of those attributes in automatically.

I have noticed that RTC will sometimes fill in attribute values for no reason and it is very confusing and frustrating. Whatsmore, the values that are sometimes filled in automatically are not associated in any way to a calculated value!  They are manual input fields that get re-arranged.  Also, in some cases, a manual field X where I insert a value after save will somehow transfer to manual field Y!

Please take an example of the work item history that I have edited and you can see here: http://i.imgur.com/iyQR7L8.png   At the bottom, I change the attribute "Change Request_C" from value "1" to "Unassigned" (removing it).  Two more history entries then occur where the value "Change Request_C" is not touched.  The latest history entry shows I have to change the attribute "Change Request_C" from value "1" to "Unassigned" again even though it was not set from "Unassigned" to "1" anywhere in between!

What is going on?

Regards,

Andrew